Nonaqueous electrolyte secondary batteries containing a positive electrode and a negative electrode, which allows lithium ions to be inserted and extracted, have been widely spread in various fields including electric automobiles, power storage systems and information devices as a battery having a high energy density. Accordingly, demands on such batteries have increased, and studies thereof have gathered pace.
In order to use the nonaqueous electrolyte secondary battery for a power source for an electric automobile, it is required that an energy density is high, i.e., a discharge capacity per unit weight or unit volume is large.
On the other hand, the safety becomes an issue as the discharge capacity per unit weight or unit volume becomes larger, and a secondary battery having a more excellent safety is required. One answer to solve the problem described above is an all solid secondary battery. The all solid secondary battery is a secondary battery using a solid electrolyte, literally, instead of an organic electrolytic solution in a nonaqueous electrolyte secondary battery, which has been used up till now. The organic electrolytic solution is flammable, and thus technological developments to improve the safety when the organic electrolytic solution is used are energetically performed. Nevertheless, it is difficult to secure the sufficient safety. The all solid secondary battery does not use the organic electrolytic solution, and thus cannot be ignited. Thus, the all solid secondary battery is a secondary battery having the very high safety.
Further, according to the all solid secondary battery, a bipolar battery can be preferably formed by coating a slurry on an electrode having a bipolar structure, obtained by forming a positive electrode and a negative electrode on both sides of a current collector, to form a solid electrolyte layer and stack it thereon, because the all solid secondary battery does not use the electrolytic solution. In such a bipolar battery, a voltage can be easily increased inside a cell.